The flowers are usually white to pink, with five petals and five sepals. They are borne singly, or in umbels of two to six or sometimes more on racemes. The fruit is a drupe (a "prune") with a relatively large hard coated seed (a "stone"). Leaves are simple and usually lanceolate, unlobed and toothed along the margin.

Many species produce hydrogen cyanide, usually in their leaves and seeds. This gives a characteristic taste in small (trace) quantities, and becomes bitter in larger quantities.

Etymology

The word is infrequent in original Latin. Pliny uses prūnus silvestris to mean the blackthorn. The English word prune is derived from the same source.

The Online Etymological Dictionary presents the customary derivations of plum and prune from Latin prūnum, the plum, which is frequent in a number of authors, including Pliny. The word is not native Latin, but is a loan from Greek προῦνον (prounon) which is a variant of προῦμνον (proumnon), origin unknown. Most dictionaries follow Hoffman, Etymologisches Wörterbuch des Grieschischen, in making it a loan from a pre-Greek language of Asia Minor, related to Phrygian.

The first use of Prunus as a genus name belongs to Linnaeus in Hortus Cliffortianus of 1737, which went on to become Species Plantarum. In that work Linnaeus attributes the word to "Varr.", who it is assumed must be Marcus Terentius Varro.

Classification

Linnean classification

In 1737 Linnaeus used four genera to include the species of modern Prunus — Amygdalus, Cerasus, Prunus and Padus — but simplified it to Amygdalus and Prunus in 1758. Since then the various genera of Linnaeus and others have become subgenera and sections, as it clearer that all the species are more closely related. Liberty Hyde Bailey says:

"The numerous forms grade into each other so imperceptibly and inextricably that the genus cannot be readily broken up into species.

Modern classification

A recent DNA study of 48 species concluded that Prunus is monophyletic and is descended from some Eurasian ancestor.

Historical treatments break the genus up into several different genera, but this segregation is not currently widely recognised other than at the subgeneric rank. ITIS recognises just the single genus Prunus, with an open list of species, all of which are shown below, under "Species".

One standard contemporaneous treatment of subgenera derives from the work of Alfred Rehder in 1940. Rehder hypothesized five subgenera: Amygdalus, Prunus, Cerasus, Padus and Laurocerasus. To them C. Ingram added Lithocerasus. The six contemporaneous subgenera are described as follows:

Prunus subgenera:

Subgenus Amygdalus: almonds and peaches. Axillary buds in threes (vegetative bud central, two flower buds to sides). Flowers in early spring, sessile or nearly so, not on leafed shoots. Fruit with a groove along one side; stone deeply grooved. Type species Prunus dulcis (Almond).

Subgenus Prunus: plums and apricots. Axillary buds solitary. Flowers in early spring stalked, not on leafed shoots. Fruit with a groove along one side; stone rough. Type species Prunus domestica (Plum).

Another recent DNA study found that Amygdaloideae can be divided into two clades: Prunus-Maddenia, with Maddenia basal within Prunus, and Exochorda-Oemleria-Prinsepia. Prunus can be divided into two clades: Amygdalus-Prunus and Cerasus-Laurocerasus-Padus. Yet another study adds Empectocladus as a subgenus to the former.

There are also a number of species, hybrids, and cultivars grown as ornamental plants, usually for their profusion of flowers, sometimes for ornamental foliage and shape, occasionally for their bark. These ornamentals include the group that may be collectively called flowering cherries (including sakura, the Japanese flowering cherries).

Other species such as blackthorn are grown for hedging, game cover, and other utilitarian purposes.

The wood of some species is a minor and specialised timber (cherry wood), usually from larger tree species such as the wild cherry.

Many species produce an aromatic resin from wounds in the trunk; this is sometimes used medicinally. There are other minor uses, including dye production.

Palaeobotanical models

The earliest fossil Prunus are wood, drupe and seed and a leaf from the middle Eocene of the Princeton Chert of British Columbia. Using the known age as calibration data, recent research by Oh and Potter reconstructs a partial phylogeny of some Rosaceae from a number of nucleotide sequences. According to this study Prunus and its "sister clade" Maloideae (apple subfamily) diverged at 44.3 mya (well before most of the Primates existed). This date is within the Lutetian, or older middle Eocene. Stokey and Wehr report: "The Eocene was a time of rapid evolution and diversification in Angiosperm families such as the Rosaceae ...."

The Princeton finds are among a large number of Angiosperm fossils from the Okanagan Highlands dating to the late early and middle Eocene. Crataegus is found at three locations: Mcabee, Republic and Princeton, while Prunus is found at those locations and Quilchena and Chuchua. A recent recapitulation of research on the topic reports that the Rosaceae were more diverse at higher altitudes. The Okanagan formations date to as early as 52 mya, but the 44.3 mya data, which is approximate, depending on assumptions, might still apply. The authors assert: "... the McAbee flora records a diverse early middle Eocene angiosperm-dominated forest.